In Michigan laws like that usually state you must store the firearm "separate from the ammunition". Having a loaded mag w/o one in the chamber would not count. Are you sure there isn't a similar law in IL?

Illinois law does not prohibit transporting a firearm and ammunition in the same case so long as the firearm is not loaded. For example, transporting an unloaded revolver and a box of ammunition in a handgun case would be perfectly legal so long as the transporter has a valid FOID card, the firearm is not readily accessible, and no local laws are violated. The issue here is whether or not a loaded magazine constitutes a loaded firearm. Another issue that I can see with this particular instance is that the loaded magazine is "in" the gun even though it is not in a position that would allow the gun to operate. The mere fact that a loaded magazine is inserted into some part of the gun may be enough to be viewed as a loaded firearm.